This invention relates generally to a method and apparatus for keeping a probe accurately positioned relative to a device to be tested and more particularly concerns a method and apparatus for accounting for drift in a high resolution probe station having motor driven stage elements or positioning components.
Probe stations are used to test a variety of integrated circuit specimen and typically include a carrier, such as a chuck, for supporting the specimen and probes for applying and receiving various forms of test signals to or from the specimen. Presently, probe stations are provided in a variety of configurations and with a variety of optional features in order to allow for highly accurate testing of numerous types of integrated circuit specimen such as semiconductor wafers. For example, the probe station itself may be an open-air probe station wherein the manipulators and specimen (or Device-Under-Test (DUT)) are exposed to ambient conditions and viewed with an optical microscope. Alternatively, the probe station may be a totally enclosed structure wherein the manipulators and specimen are contained within a vacuum chamber and viewed with a high resolution microscope, such as a Scanning Electron Microscope (SEM), a Focus Ion Beam (FIB) system, or the like.
The probe station may also include a variety of optional features such as movable platform, carrier and manipulator stage elements, thermal components and environmental controls. In addition, the components of the probe station may have a variety of structural arrangements to allow for different wiring schemes or configurations, such as coaxial and triaxial shielding and guarding arrangements. These configurations and features allow the probe station to test the DUT with a minimal amount of interference (e.g., from noise, etc.) and at or near real-life operating conditions, (e.g., at temperature). For example, a high resolution probe station using a SEM and motor driven platform, carrier and manipulator stage elements to view and test a specimen in a vacuum chamber is capable of greatly reducing (if not eliminating) the effect of noise induced by light and vibration so that highly accurate testing of the specimen may be accomplished. The probe station can further increase the accuracy of the specimen testing by triaxially wiring the probe station and components to eliminate the noise associated with unshielded or unguarded signal lines (e.g., parasitic capacitance, electromagnetic interference (EMI), etc.).
Although these achievements have greatly improved the accuracy with which specimen may be tested via a probe station, they have not eliminated all areas in which improvements are needed. For example, the accuracy of probe stations remains affected by the environmental conditions within which the apparatus is operated. More particularly, environmental conditions, such as thermal buildup, can cause the movable components of the probe station to make unwanted movements, such as drift and wobble. These movements are most noticeable in high resolution probe stations having vacuum enclosures due to the lack of ventilation within the probe station housing and the resolution capabilities of the microscope and components.
Accordingly, it has been determined that the need exists for an improved method and apparatus for keeping a probe accurately positioned on a specimen which overcomes the aforementioned limitations and which further provides capabilities, features and functions, not available in current probe station apparatus and methods.